The objective of the proposed research is to investigate the early organizational effects of steroid hormones on spatial memory of rats. Preliminary results indicate that exposure to gonadal steroids or exogenous estradiol benzoate improves the acquisition of a radial maze task for both working and reference memory components, when rats are tested as adults. The experiments described here seek to determine the hormonal and temporal specificity of estrogen and androgen action. In addition, we have found that early steroid exposure causes rats to preferentially attend to or use geometry rather than landmark cues to solve the task. This preferential use of geometry is highly correlated with brain lateralization, as indexed by degree of turning bias. The second aim of the current proposal is to evaluate this hypothesis and to determine whether rats exposed to gonadal steroids during the first postnatal week are more accurate during acquisition of a radial maze task because increased lateralization allows geometry cues to overshadow landmark cues and thereby simplify the task. These data are particularly intriguing in light of recent findings that receptors for estrogen, and androgens are present in hippocampus and frontal cortex of neonatal rats, and that these brain areas are involved in the control of working and reference memory, respectively. An investigation of the organizational effects of sex steroids on spatial ability should provide: 1) an animal model for determining the proximate physiological cause of sex differences in spatial ability, and 2) a better understanding of how the hippocampus and frontal cortex are organized to process and retain spatial information required to guide behavior.